1. Field of the Invention
The invention relates to a sealing configuration for a passage of a shaft having an axis through a stationary casing enclosing an inner space to which a fluid can be admitted and from which the shaft emerges, the sealing configuration having a vapor chamber surrounding the shaft and being open to the surroundings, and having seals adjacent the vapor chamber on both sides along the axis for admitting the fluid to the vapor chamber through at least one of the seals. The invention also relates to a method for operating such a sealing configuration.
Such a sealing configuration and a method for its operation are disclosed in German Patent DE-PS 576 969.
The invention particularly relates to a sealing configuration for application to a steam turbine in order to seal a passage for a rotating shaft from a casing of the steam turbine. In it, steam which emerges along the shaft from the housing through a seal is collected in a vapor chamber and released into the surroundings. Due to condensation, the steam is converted into a mist and is therefore visible at the sealing configuration as a "vapor image". It thus offers a simple functional check for the sealing configuration. Such a simple functional check is particularly interesting and desirable, in many cases, on a steam turbine for industrial purposes having a power output which is generally between approximately 1 MW and approximately 50 MW. In such a steam turbine, the pollution of the surroundings due to a vapor image is generally within acceptable limits.
Sealing configurations for passages or ducts for shafts are known in many forms in the prior art. In particular, there is a large number of embodiment possibilities for the individual components of the sealing configurations, in particular the seals themselves. Sealing configurations for use on steam turbines appear in German Published, Non-Prosecuted Patent Applications DE 26 43 484 A1 and DE 33 33 530 A1. Various embodiment possibilities for components of the sealing configurations are also described in those publications. Published European Patent Application 0 463 532 A1 concerns the removal of steam which emerges from a sealing configuration, with that steam being condensed in a so-called "vapor condenser configuration". The main feature in that publication is the configuration of the vapor condenser itself. In other words, in particular, it is constructed as an unpressurized heat exchanger, which means that the condensation of the vapor in it takes place at approximately normal atmospheric pressure. No release of vapor into the surroundings takes place since the vapor is completely condensed.
British Patent Specification 1 267 548 likewise concerns a sealing configuration on a steam turbine of the type which is described in Published European Patent Application 0 463 532 A1. That sealing configuration is to be usable not only on a passage for a rotating shaft, in particular a driven shaft of a steam turbine, but also on a passage for a valve spindle which can be displaced along its axis and is not necessarily rotatable. In that sense, the concept of a "shaft" is to be understood herein in such a way that it includes both rotatable shafts and displaceable spindles.
The function and structure of seals for sealing configurations of the type described are disclosed in the book entitled "Thermische Turbomaschinen" [Thermal Turbomachines] by W. Traupel, Springer-Verlag, Berlin 1977, Volume 1, Chapter 10. In particular, seals of the labyrinth seal type are described in detail. Other seals, namely stuffing box seals, in particular stuffing box seals with carbon rings, are only mentioned in passing and are designated as being disadvantageous for steam turbines in power stations. That comment, however, naturally does not refer to the use of stuffing boxes and/or carbon rings in seals for steam turbines which are intended for industrial purposes. It is seen from German Published, Non-Prosecuted Patent Applications DE 26 43 484 A1 and DE 33 33 530 A1 that carbon ring seals are demonstrably very common in such steam turbines.
A sealing configuration of the type mentioned at the outset, along with a method for executing it, is disclosed in German Patent DE-PS 567 969. In connection with the device described therein, it has been additionally provided to charge several vapor chambers in various sealing configurations with a fluid, namely steam, from a single source. That device is intended to provide relief of the environment from vapor chamber steam, since in order to assure sufficient overpressure in each vapor chamber it is only necessary that fluid flow from a single scaling configuration, namely the sealing configuration in which the fluid encounters the least resistance between the vapor chamber and the flue through which the fluid is exhausted.
German Patent DE-PS 451 680 relates to a differently constructed sealing configuration. In that sealing configuration a vacuum is maintained in a chamber surrounding the shaft, which is located farthest away from the shaft along it and which vacuum causes air to be sucked along the shaft into the chamber. That is intended to assure that no steam at all reaches the environment. The vacuum is produced by an appropriately provided aspirating device, which moves the mixture of air and steam formed in the chamber away into a flue or into a recovery installation.
As was already stated, some pollution of the surroundings with vapor always appears at a sealing configuration of the type described at the outset and that pollution can, under certain circumstances, make special configurations necessary for keeping the air pure. In addition, a functional check using a vapor image can only have limited reliability because it is not easy to recognize small changes. The functional check must, therefore, essentially be limited to determining whether or not damage to a sealing configuration has already occurred. Regular diagnosis of the shaft sealing configuration, with the objective of obtaining a quantitative conclusion on the functional capability of the sealing configuration and of recognizing damage even in its incipient stage, is impossible in the prior art.